QRZ! Ham Radio 4/QRZ Ham Radio Callsign Database - Volume 4.iso/digests/antenna/940142.txt

Internet Message Format | 1994-11-13 | 16KB

Date: Sat, 14 May 94 04:30:09 PDT
From: Ham-Ant Mailing List and Newsgroup <[e-mail]>
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Subject: Ham-Ant Digest V94 #142
To: Ham-Ant


Ham-Ant Digest              Sat, 14 May 94       Volume 94 : Issue  142

Today's Topics:
                             Loop Skywire
                      More AM STATIONS help....
                       radar detectors (3 msgs)
                recommendation for high gain 2M mobile
                              Wind loads

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We trust that readers are intelligent enough to realize that all text
herein consists of personal comments and does not represent the official
policies or positions of any party.  Your mileage may vary.  So there.
----------------------------------------------------------------------

Date: Thu, 12 May 1994 14:10:08 GMT
From: ihnp4.ucsd.edu!newshub.sdsu.edu!nic-nac.CSU.net!usc!howland.reston.ans.net!EU.net!sunic!psinntp!psinntp!arrl.org![e-mail]
Subject: Loop Skywire
To: [e-mail]

Jim Grubs, W8GRT ([e-mail]) wrote:

: > One thing to be carful of is to make it as close to a square as possible. Too
: > far from a square and it starts to exhibit some sharp lobes, depending on the
: > exact configuration and frequency, height, etc. Actually, I think a circle
: > would be best but that's pretty hard to do for most of us. Mine was within a
: > few feet of being square.
:
: I saw a loop demo at Dayton 10 or 12 years ago that pretty well
: proved that loop shape doesn't make a darn bit of difference if
: the circumference is << lambda/2.

True, for very small loops the shape doesn't affect the pattern, though
I can think of some shapes that could increase the losses.

However, the loop being discussed is a full wavelength at the lowest
frequency, and multiple wavelenths at harmonic frequencies.  Thus,
shape does make a difference in the actual pattern.  On the other
hand, the actual pattern is often unpredictable, given the amount
of interfering objects such an antenna normally encounters.
--
Zack Lau  KH6CP/1           2 way QRP WAS
                           8 States on 10 GHz
Internet: [e-mail]   10 grids on 2304 MHz

------------------------------

Date: 12 May 94 05:04:41 GMT
From: agate!howland.reston.ans.net!darwin.sura.net!mother.usf.edu!luna![e-mail]
Subject: More AM STATIONS help....
To: [e-mail]

First, Thank you to everyone who help me with the AM Station questions.
OKay, I've read Answers to Frequency asked Questions about long-distance
reception of local AM ... stations.

  So, I've become very interested in this topic, and have began to TRY and
pick up some stations.

Here is where I would like more help with.

I own a DENON model DRA-25 (140W) receiver with digital display.

On the back there is an ANTENNA TERMINALS section.
       It looks like this...

  --------------ANTENNA TERMINALS-----------

     FM              GAD    AM

    300 ohms  75 ohms 3     3

    /-------/ /-----/ 3     3
   (0)      (0)      (0)   (0)
                     LOOP ANT



(0) represents where a wire should go.....
/-----/ represents diagrams shown on back.....


Now, what I would like to know is WHAT and HOW I should go about setting
this up so that I can TRY and get some stations.  I really want to get
700 WNW (I live in Tampa, Florida it is a Cincinnati station).  Someone
suggested copper wire.  What size?

Or is there an antenna I should seek out and try and
buy?  Or can someone send me a diagram on HOW to make an antenna.  I've
really enjoyed trying to get some stations, I find it fascinating, and
would like to try it somemore, however, it has gotten frustrating without
having a good antenna setup.  It was cool getting stations in NY,
Nashville, and Louisiana though!  Any help would be great!  Oh, also,
there is a Spanish Station I get right near 700, is there a way to (mask)
that station out?

Thanks again... Sorry for all the newbie questions.


------------------------------

Date: Thu, 12 May 1994 14:01:42 GMT
From: ihnp4.ucsd.edu!newshub.sdsu.edu!nic-nac.CSU.net!usc!howland.reston.ans.net!EU.net!sunic!psinntp!psinntp!arrl.org![e-mail]
Subject: radar detectors
To: [e-mail]

Ken A. Nishimura ([e-mail]) wrote:
: In article <[e-mail]>,
: MORROW  J  <[e-mail]> wrote:

: > Firstly, in order to detect a specific frequency, how is this
: > accomplished?  Does the detector produce a matching frequency to
: > compare with the incoming radar signal?

: Same way that most all radios tune a specific station.  Most
: all radar detectors are superhet receivers.  For example, let's
: say you are looking for a 24.150 GHz K band radar.... You would
: locally generate a frequency (LO) say 25.150 GHz and mix it in
: a microwave diode.  Then you would look for a 1 GHz mix product,
: which is then filtered and detected.  You can tune around the
: frequencies of interest by tuning the LO, so if you wanted to
: look for Ka band, you would retune your LO to 35 - 38 GHz.
: I doubt any detectors out there are using direct conversion.


: >Can police "electronically" determine if you possess a
: >radar detector?

: Yup, those Canadian cops have them.  Every superhet receiver
: leaks a bit of LO, as no mixer has infinite reverse isolation.
: Radar detectors are real bad since they use a passive mixer

There are balanced passive mixers with fairly decent LO rejection.
One of the biggest 10 GHz amateur station relies on mixer LO
rejection--his IF is 28 MHz.   On the other hand, there are
some active mixers that don't do such a great job of isolating
the LO from the IF port.

: due to the high frequencies.  The LO goes right back out the
: antenna.  Some real cheap units will set off another detector.

: >If so, is there a method to mask the radiation emitted
: >from the detector, but still ensure its sensitivity? For example, wrap
: >the detector in aluminum foil leaving only the front (the horn style
: >antenna) exposed.

: Wrapping the device may help a bit, but since the LO goes out
: the antenna, it's tough.  Some detectors which use low side
: injection (LO lower than desired RF) will make the waveguide
: from the antenna to the diode just above cutoff, so that the lower
: frequency LO doesn't go back out.  This only works for single
: band devices.  Other ways are using a perturbation (i.e. screw)
: in the waveguide to notch out the LO frequency.  This works
: to an extent.

A neat device that increases the LO isolation by 20 dB with only
0.5 dB loss (typical) is a ferrite isolator.  New, these devices
sell for $100 or more.  But, you can buy mystery isolators of
unknown frequency coverage quite inexpensively :-).

The best solution may be to use a PHEMT preamplifier, which often
has quite a bit of reverse isolation.  In addition, you can increase
the sensitivity of a 10 or 24 GHz receiver by 10 dB or more.  A
difficulty is at 24 GHz, it is generally accepted by many amateurs
that devices will vary too much to allow easily copied designs,
unless you use transistor chips and lead bonding equipment.

You can also make bandpass filters out of a section of waveguide.
You essentially convert the waveguide into a series of tuned cavities.

: >Is there a method of making it undetectable and perhaps stealthy?

: Change the LO.  Those radar detector detectors are also superhet
: devices, that look for the LO that most units use.  If you want
: to spend the money and effort, you can make your detector use
: a non-standard LO.  You could also make a radar
: detector detector detector on the same principle.  Look for
: the cop's LO.

This wouldn't work if the radar detector was looking for the
second local oscillator.  Many detectors have a swept second
local oscillator that allows the radar detector to function
as a scanner.

One thing that people don't realize is how weak a signal one
can detect with a good microwave receiver.  For instance, WA1OUB
could hear K1WHS running just -60 dBm, or 1 nanowatt, on 1296 MHz,
even though they were about 60 miles apart!   Sheet metal
shielding probably isn't good enough to really isolate a typical
oscillator over short distances (few hundred feet)  Lossy materials,
such as trees and concrete, seem to do a much better job at
microwaves.
--
Zack Lau  KH6CP/1           2 way QRP WAS
                           8 States on 10 GHz
Internet: [e-mail]   10 grids on 2304 MHz

------------------------------

Date: Thu, 12 May 1994 18:30:40 GMT
From: gatekeeper.us.oracle.com!barrnet.net!netnews.synoptics.com![e-mail]
Subject: radar detectors
To: [e-mail]

>I won't go into details since I may be abetting a crime, but
>I think you get the drift.  Since we are on the
>subject, the above is for education only, and I do NOT
>recommend that you do any of the above.  Drive at
>or below the speed limit.
>
>-Ken

If you drive below the limit stay out my way :>)
Dave

------------------------------

Date: Thu, 12 May 94 02:04:39 GMT
From: ihnp4.ucsd.edu!dog.ee.lbl.gov!agate!howland.reston.ans.net!gatech!newsfeed.pitt.edu!dsinc!wells!w2up![e-mail]
Subject: radar detectors
To: [e-mail]

MORROW  J <[e-mail]> writes:

> I have many questions about the operation of radar detector. Firstly,
> in order to detect a specific frequency, how is this accomplished?  Does
> the detector produce a matching frequency to compare with the incoming
> radar signal?  Can police "electronically" determine if you possess a
> radar detector? If so, is there a method to mask the radiation emitted
> from the detector, but still ensure its sensitivity? For example, wrap
> the detector in aluminum foil leaving only the front (the horn style
> antenna) exposed. Is there a method of making it undetectable
> and perhaps stealthy?
>

I believe it's just a wideband receiver. Yes, they can determine if you
have a radar detector. I've seen some advertised that claim to be
detect-proof, but don't remember details or names.


=======================================================================
Barry N. Kutner, W2UP       Usenet/Internet: [e-mail]
Newtown, PA                 Packet Radio: W2UP @ WB3JOE.#EPA.PA.USA.NA
                            Packet Cluster: W2UP >K2TW (FRC)
.......................................................................

------------------------------

Date: Thu, 12 May 1994 22:55:39 GMT
From: ihnp4.ucsd.edu!news.acns.nwu.edu!math.ohio-state.edu!howland.reston.ans.net!vixen.cso.uiuc.edu!milo.mcs.anl.gov!anagram.mcs.anl.gov![e-mail]
Subject: recommendation for high gain 2M mobile
To: [e-mail]

I am looking for suggestions for high gain 2M mobile antennas.  dual banders
would be nice (70cm).  I live in the mountians and we need all the gain
we can get.
[e-mail]

------------------------------

Date: Wed, 11 May 1994 09:34:39 -0400
From: ihnp4.ucsd.edu!dog.ee.lbl.gov!agate!howland.reston.ans.net!math.ohio-state.edu!news.acns.nwu.edu!ftpbox!mothost!lmpsbbs!NewsWatcher![e-mail]
Subject: Wind loads
To: [e-mail]

In article <2qma5e$[e-mail]>, [e-mail]
(Ronald Viegelahn) wrote:

>
>
>  Can anyone provide the answer to the following 2 questions ?
>
> 1: How many psi does a 100 mph wind generate at sea level ?

Courtesy of the Commercial Products book from Rohn Towers (1991),
the answer is 40 psf, or 0.27777 psi. when measured 30 feet above
the ground surface in an unobstructed flow.

>
> 2: How much does 1 cubic yard of concrete weight ?

Same source, 3,780# for a 3,000 psi mix, which is the absolute
minimum acceptable for the Rohn foundation designs.

>
>                     73
>
>                     [e-mail]

However, several words of caution:
A)  The recommended maximum design wind speeds were changed in
RS-222D/ ANSI A58.1-1982. Your local building code may not reflect
the current commercial practice standards.
B)  Local or state building codes for earthquake design requirements
may significantly alter the foundation design normally recomended by
the tower manufacturer.
C)  When evaluating the cross-sectional area of the antenna, remember
that the worst case windloading usually will occur when the antenna is
at an angle to the wind, not facing directly into the wind. You must
first calculate both the head-on and right angle loads, then compute
the worst case load from there.

--
Karl Beckman, P.E.         < The difference between genius and stupidity >
Motorola Comm - Fixed Data < is that genius has its limits.     -Unknown >

The statements and opinions expressed here are not those of Motorola Inc.
Amateur radio WA8NVW @ K8MR.NEOH.USA.NA         NavyMARS VBH @ NOGBN.NOASI

------------------------------

Date: 12 May 1994 01:40:09 -0600
From: mnemosyne.cs.du.edu!nyx.cs.du.edu![e-mail]
To: [e-mail]

References <[e-mail]>, <D>, <[e-mail]>nd.r
Subject : Re: kites <--> antennas ?

Out of interest, there is an International Kite Festival on 21/22 May at
the Isle of Wight, England. This information comes from Radio Communications
magazine, as the Wireless Museum will be using kite aerials.

Sadly, I probably won't be able to make it either...

David

------------------------------

Date: 12 May 1994 21:05:42 GMT
From: ihnp4.ucsd.edu!newshub.sdsu.edu!nic-nac.CSU.net!usc!howland.reston.ans.net!vixen.cso.uiuc.edu!bradley.bradley.edu!augustana.edu![e-mail]
To: [e-mail]

References <[e-mail]>, <[e-mail]>, <[e-mail]>bradley
Subject : Re: Multiple Loops? (was Loop Skywire)

In article <[e-mail]> [e-mail] (Zack Lau (KH6CP))
writes:

>However, the loop being discussed is a full wavelength at the lowest
>frequency, and multiple wavelenths at harmonic frequencies.  Thus,
>shape does make a difference in the actual pattern.  On the other
>hand, the actual pattern is often unpredictable, given the amount
>of interfering objects such an antenna normally encounters.

This is a lot of wire, but would it be feasible/desirable
to have loops suspended within the loop, one for each band
of interest?  I assume there would be interactions between
the loops, but maybe to your advantange as you could build
an effectively larger loop through combinations of the
loops.  I thinking here of squares within the square.

Just curious....

Kevin, KB9IUA
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Kevin L. Anderson,     Geography Dept.,     Augustana College
Rock Island, Illinois   61201   USA     phone: [phone]
e-mail: [e-mail]  or [e-mail]
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

------------------------------

End of Ham-Ant Digest V94 #142
******************************